(L-R) Canada''s Prime Minister Stephen Harper, U.S. President Barack Obama, European Council President Herman Van Rompuy, Germany''s Chancellor Angela Merkel and Britain''s Prime Minister David Cameron pose for a group photo during a G7 leaders meeting at European Council headquarters in Brussels.

The United States and its allies used the first Group of Seven meeting without Russia in 17 years to condemn Moscow's actions in Ukraine and threaten hard-hitting sanctions if President Vladimir Putin does not help restore stability.

Meeting in Brussels rather than the Black Sea resort of Sochi - a snub to Russia which was supposed to have hosted the G8 - Western powers and Japan delivered strong rhetoric, even if the EU's commitment to further sanctions remains in doubt.

"We are united in condemning the Russian Federation's continuing violation of the sovereignty and territorial integrity of Ukraine," the United States, Germany, Japan, France, Britain, Italy and Canada said in a joint statement.

"Russia's illegal annexation of Crimea, and actions to destabilize eastern Ukraine, are unacceptable and must stop."

That message was reinforce by President Barack Obama, who said Russia's economy was already suffering and would only suffer more if Putin did not change behavior.

"If Russia's provocations continue, it's clear from our discussions here that the G7 nations are ready to impose additional costs on Russia," he said. "Today, in contrast to a growing global economy, a sluggish Russian economy is even weaker because of the choices made by Russia's leadership."

Putin, who will meet Germany's Angela Merkel, French President Francois Hollande and Britain's David Cameron on the sidelines of 70th anniversary of the D-Day landings in France tomorrow, appeared unfazed by the threats.

Asked at an event in St. Petersburg how he felt about being excluded from the G8 for the first time since joining the club in 1997, Putin was typically pointed, barely breaking stride to speak to Kremlin reporters as he left a meeting.

"I would like to wish them bon appetit," he said, before walking away swiftly.

It appears unlikely that Obama and Putin will talk in France.

"Should we have the opportunity to talk, I will be repeating the same message that I've been delivering to him throughout this crisis," Obama said.